Liquified gas delivery system



April 29, 1969 I w. A. DAVIES-WHITE 3,440,829

LIQUIFIED GAS DELIVERY SYSTEM Filed Dec. 11. 1963 INVENTOR.

WILLIAM A. DAVIES-WHITE United States Patent 3,440,829 LIQUIFIED GASDELIVERY SYSTEM William A. Davies-White, San Pablo, Calih, assignor toLaboratory for Electronics, Inc., Boston, Mass., a corporation ofDelaware Filed Dec. 11, 1963, Ser. No. 329,779 The portion of the termof the patent subsequent to Mar. 14, 1983, has been disclaimed Int. Cl.F17c 7/02, 7/00 U.S. Cl. 6251 1 Claim ABSTRACT OF THE DISCLOSURE Thisinvention relates generally to liquified gas delivery systems and, moreparticularly, it is concerned with the controlled withdrawal of aliquified gas from an insulated storage vessel.

Customarily, liquified gases, such as liquid nitrogen, are stored ininsulated containers known as Dewar flasks so as to minimize wastage dueto evaporation. That is to say, as the liquid evaporates, it createsconsiderable pressure, and in order to limit this pressure to a safevalue, some of the liquid which has evaporated must be released byventing. If the demand for the liquid is constant and precisely known, afixed rate of evaporation can be established consistent with thepressure limiting elfect of deplenishing the supply so that the pressureseldom, if ever becomes excessive. The difficulty, however, is thatthere are many applications for liquified gases where the demand isunpredictable and inconstant. Moreover, a fixed rate of evaporation isoftentimes difficult to establish because it depends so much on ambienttemperature and pressure conditions.

Hitherto, a common practice has been to try to minimize, so far aspossible, the rate of evaporation during the intervals when the liquidis not being used, and to pressurize the container or vessel with a likegas obtained from an external source in order to boost the pressure inthe container to the level needed to force out the liquid whenever itsuse is called for. This requires the attention of an operator and, ofcourse, a separate vessel to contain the gas which is used forpressurizing. Another common practice which avoids this disadvantage isto provide a heating coil for heating the liquified gas in the storagevessel and thereby accelerate the process of evaporation whenever ademand for the liquid exists. The problem with this device is that theamount of heat provided must be closely controlled in accordance withthe rate at which the liquid is withdrawn, and if the latter isinconstant, such control may be diflicult to implement as a practicalmatter.

An object of the present invention, therefore, is to provide an improvedliquified gas delivery system which is adapted to ensure the dischargeof an adequate amount of liquid to meet current demands irrespective ofthe rate at which the demand is made.

Another object is to accomplish the foregoing object without appreciablewastage due to venting for pressure relief.

Still another object of the invention is to provide a liquified gasdelivery system which is relatively simple to construct in that it doesnot depend on the use of controls which are functionally related to theutilization device for the gaseous liquid.

A further object is to provide a liquified gas delivery system which isreliable and safe to operate.

The novel features of the invention, together with further objects andadvantages, will become apparent from the following detailed descriptionof a preferred embodiment and from the drawing to which the descriptionrefers.

In the drawing the liquified gas delivery system of the invention isshown schematically.

With reference now to the drawing, it will be observed that the numeral11 designates a vacuum flask containing a liquified gas 12, such asliquid nitrogen. Although the invention is not limited to use with anyspecial type of container or flask, a Dewar flask is most commonly usedfor this purpose both in the laboratory and by commercial suppliers, andthe delivery system of the invention is specifically designed to be usedwith this type of flask. As shown, a Dewar flask is characterized by adoublewalled liner 13 which is coated with heat reflective material andwhich is evacuated so that the interspace between the walls acts as agood heat insulator. Access to the interior of the flask is had througha neck portion at the top, and the fact that this is the only opening inthe flask minimizes the problem of evaporation due to the transfer ofheat from outside the flask. Most commonly the liner is mounted in ametal bell 14 which protects it from damage.

To couple the delivery system of the invention to the flask, anapcrtured stopper 16 is fitted to the mouth and a hollow cylindricalmember 17 is in turn fitted to the aperture in the stopper. Member 17extends above the stopper for a short distance and at the top is cappedby a cover disc 18. The supply line is designated 19 in the drawing andhas its inlet end 19' located near the bottom of the flask. To admit thesupply line, to the interior of the flask, a central aperture isprovided in the disc 18.

Exteriorly of the flask, the supply line undergoes a right angle bend soas to aflFord a horizontal run to its outlet end 19". A cup 21 issuspended from this horizontal run of the supply line and a check valve22 is provided between the cup and the bend. Check valve 22 preventspressure fluid from flowing backward into the flask, as will beexplained more fully in connection with the operation of the system.

Coupled to line 19 at a point directly above the cup is an auxiliaryline 23 which leads back to the mouth of the flask. More specifically,an aperture is provided in the wall of member 17 to receive a line 24terminating the auxiliary line. At the outlet end of line 24 there is asafety valve 25. Also a check valve 26 is disposed in the auxiliary line23 to prevent the flow of pressure fluid out of the flask by Way of theauxiliary line and a control valve 27 is provided between cup 21 and theoutlet end of the supply line to control the discharge of the liquidfrom the system.

In operation, when a charge of liquified gas is called for, controlvalve 27 is opened permitting gas to flow out of the flask by way of thesupply line. There is no flow through the auxiliary line because thesense of check valve 26 is opposite to that of check valve 22. In thefirst instance, it will be assumed that the pressure in the flaskresulting from the normal evaporative process is sufficient to producean adequate charge of liquified gas to satisfy the demand of theutilization device to which the outlet end of the supply line isconnected. The latter may be a cold chamber, for example, and the valve27 may be automatically controlled by a thermostat in the cold chamber.

After the required amount of liquid has been withdrawn from the flaskand the control valve is closed, a small quantity of the liquid willhave been trapped in the cup 21. The cup liquid absorbs heat from thesurrounding atmosphere a good deal faster than does the liquid in theflask because the cup is not insulated. In fact, it is preferred to formthe cup from a relatively good heat conductor, such as copper, so thatthe cup liquid evaporates and builds up vapor pressure at a relativelyrapid rate. The vapor or gaseous phase fluid from the cup is preventedfrom entering the flask by way of the supply line because of the actionof check valve 22. Instead, it flows through the auxiliary line 23 intothe space above the level of the liquid in the flask where it createsadditional pressure on the surface of the liquid. When the utilizationdevice again calls for liquid and control valve 27 is again opened,therefore, a suflicient pressure will exist to force the required amountof liquid out of the flask to meet the additional demand. Also, theliquid in the cup 21 will be replenished in the course of the liquidflow through the supply line so that the process can be repeated. Inother words, the pressure in the flask is maintained according to theinvention without the need for any external pressurizing pro cedure oradjustments by an attendant.

Should the demand of the utilization device temporarily become lowerthan normal or cease to exist, permitting the pressure to continue toincrease, relief is provided by the safety valve 25. It should be noted,however, that under these circumstances, only a relatively small amountof the liquid will be lost because the cup 21 is not replenished and assoon as all the cup liquid has evaporated, no further pressure build upwill take place according to the invention. Furthermore, by appropriatedesign of the cup, the rate of evaporation can be established at anydesired value consistent with the normal demand of the utilizationdevice.

Although the invention has been described in connection with a singlepreferred embodiment, it will be appreciated that many variants of thisembodiment are possible that are within the spirit and scope of theinvention. Therefore, the invention should not be deemed to be limitedto the details of what has been described herein by way of illustration,but rather it should be deemed to be limited only to the scope of theappended claims.

What is claimed is:

1. A system for delivering liquified gas from an insulated flask to autilization device, said system comprising a supply line leading from afirst inlet point in the flask to a discharge point outside the flask,said first inlet point being located below the level of the liquid inthe flask, said discharge point communicating with said utilizationdevice, and said supply line serving to conduct the gas from said onepoint to the other while maintaining it in an essentially liquid state,means coupled to said supply line at a point outside the flask inadvance of said delivery point for trapping and collecting a smallportion of the liquified gas whenever the same is caused to flow fromsaid first inlet point through said supply line to said delivery point,said liquified gas collection means being adapted to permit heat fromthe surrounding atmosphere to raise the temperature of the liquified gascollected therein at a substantially more rapid rate than the rate atwhich the temperature of the liquified gas in the flask is raised,thereby causing the liquified gas in said collection means to evaporateand create pressure to act upon the liquified gas in the flask, and saidcollection means being further adapted to be replenished by trapping ofthe liquified gas each time the same is caused to flow through saidsupply line and past the point where said collection means is coupled, acheck valve disposed in said supply line in advance of said collectionmeans such that the liquified gas being supplied to said utilizationdevice must first pass through said check valve and then past saidcollection means, said check valve preventing gas under pressure createdby evaporation in said collection means from acting on the liquefied gassurrounding said first inlet point in the flask, a control valvedisposed in said supply line immediately preceding said discharge pointto control the discharge of liquified gas from said discharge point tosaid utilization device, an auxiliary line coupled to said supply lineat a point located between said control valve and said check valve forconducting gas under pressure from said collection means to a secondinlet point in the flask located above the level of the liquified gastherein, and a second check valve disposed in said auxiliary line, saidsecond check valve acting to prevent the gas under pressure above thelevel of the liquified gas in the flask from escaping to said supplyline and discharging through said control valve whenever the same isopen, and the opening of said control valve causing a reduction in thepressure in said supply line on the discharge side of said first checkvalve, thereby permitting a limited supply of liquified gas to flow outof said flask to said utilization device, said flow being terminated bythe resulting reduction in the pressure of the gas in the flask abovethe level of the liquified gas until said control valve again closespermitting a further build-up of the pressure of the gas due toevaporation of the liquified gas trapped by said collection means.

References Cited UNITED STATES PATENTS 2,580,649 1/1952 Bludeau 62-552,968,163 1/1961 Beckman 62-51 3,097,500 7/1963 More 62-55 2,580,7101/1952 Wildhack 62-53 3,081,602 3/1963 Ehms 62-55 3,093,974 6/1963Templer et a1 62-55 X 3,097,498 7/ 1963 Williams 62-53 X LLOYD L. KING,Primary Examiner.

US. Cl. X.R. 62-53, 55

